Osmosis

Exchange of materialsp.214

Requirements

• 24 boiling tubes• 12 cork borer • 12 tiles• 12 pens• 12 racks• Cling film• Potatoes

• Demo osmometer

• No worksheets

Objectives

• Students should learn:• that water often moves across boundaries by

osmosis and why it is important• that osmosis is the diffusion of water through a

partially-permeable membrane from a dilute to a more concentrated solution

• that differences in concentrations of solutes inside and outside cells cause water to move by osmosis.

Outcomes

• Most students should be able to:• define osmosis• distinguish between diffusion and osmosis• carry out an experiment to find out about the process

of osmosis• explain the results of experiments in terms of osmotic

movement of water.• Some students should also be able to:• explain the importance of osmosis in plants and

animals.

Specification

• Dissolved substances move by diffusion and by active transport. [B3.1.1 a)]

• Water often moves across boundaries by osmosis. Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules. [B3.1.1 b)]

• Differences in the concentrations of the solutions inside and outside a cell cause water to move into or out of the cell by osmosis. [B3.1.1 c)]

• Controlled Assessment: B4.5 Analyse and interpret primary and secondary data. [B4.5.4 a)]

Workbook

• P.101-2

Which way does the flow go?

AimsIn this activity you will think about the flow of money. This can help you to understand osmosis. TaskImagine that there are three friends, all of whom have overdrafts at the bank. They meet up and compare their finances. They decide that whoever is the most overdrawn should get money from anyone who is less in debt than they are. This means that money will move from an account where there is more money, to an account where there is less money.

In the same way, water will move across a partially permeable membrane from where there is more water to where there is less water. This is called osmosis. On the diagram below, draw an arrow to show the direction in which the water will move.

In the same way, water will move across a partially permeable membrane from where there is more water to where there is less water. This is called osmosis. On the diagram below, draw an arrow to show the direction in which the water will move.

define osmosis

• osmosis is the … of water through a … membrane from a … to a … solution

• Missing words• partially-permeable, more concentrated,

dilute, diffusion

define osmosis

• osmosis is the diffusion of water through a partially permeable membrane from a dilute to a more concentrated solution

• Missing words• partially-permeable, more concentrated,

dilute, diffusion

comparing diffusion and osmosis

• Diffusion • Osmosis

Comparing osmosis and diffusionDiffusion• Movement of any very

small particle• From a high to low

concentration• Doesn’t have to pass

through a barrier

• Kinetic energy from particles

Osmosis• Movement of water

molecules only• From a dilute to a

concentrated solution• Passes through a

partially permeable membrane

• Kinetic energy from particles

experiment to find out about the process of osmosis

visking tubing

strong sugar solution + red dye

capillary tube

The Osmometer

water

(more concentrated solution)

(dilute solution)

Partially permeable

explain the results of experiments in terms of osmotic movement of water.

The osmometer1. The water is a ……. Solution, the sugar

solution is more ………..2. The visking tubing is a ............... ............

membrane3. Water moves into the visking tubing by...........4. The bag fills out and the contents press out

on the walls. The bag is firm or ...........5. Water continues to move into the bag, The

pressure created forces the liquid up the capillary tube.

The osmometer1. The water is a dilute Solution, the sugar

solution is more concentrated solution2. The visking tubing is a partially permeable

membrane3. Water moves into the visking tubing by

osmosis4. The bag fills out and the contents press out

on the walls. The bag is firm or turgid5. Water continues to move into the bag, The

pressure created forces the liquid up the capillary tube.

explain the importance of osmosis in plants and animals.

• Read p.215

The effect of osmosis on animal and plant cells

• Animal cells• In a concentrated solution

lose water by osmosis and shrink

• In a dilute solution take in water by osmosis and burst as the cell membrane is weak

• Plant cells• In a concentrated solution

the cytoplasm and cell membrane shrink away from the cell wall = plasmolysed cell/flaccid

• In a dilute solution take in water and the cytoplasm pushes out on the cell wall = turgid/firm cell

Plasmolysis video

lettuce video

Slugmosis video

• Make a script for the video using these words

• Osmosis• Partially permeable• Diffusion of water molecules• Dilute solution• More concentrated solution

Osmosis in potato tissue

Have you ever wondered why they store the cut chips in slightly salty water in the

chip shop before they fry?

Method• Each group will need:

1. 2 x boiling tubes2. 1 x tube rack3. 1 x marker pen (?)4. 2 x potato chips (fair testing???)5. 1 x 20 cm3 syringe (for?)6. Some Cling film (?)7. Repeats / reliability (?)

• Label the boiling tubes with the treatment and your initials.• Using the syringe, add 20 cm3 of the sugar solution to each tube.• Cut the potato chips to exactly 30 mm.• Record initial length in mm on your results table.• Put the chips into the boiling tubes (one per tube) and cover with cling film.• Place tubes into your group’s tube rack and put carefully onto the side bench.

Draw a blank results table (?)

1.0 MSCC

0.0 MDBB

Table of results for osmosis in potato chips

Tube Length of chipBefore expt /mm

Length of chip after expt /mm

Change in length

Percentage change in length

AB

Formula for percentage change = change/original x100